The invention relates to magnetic particles for separating biological mixtures, to a process for preparing them and to a use of the magnetic particles.
From U.S. Pat. No. 3,970,518 it is known to use magnetic particles having different magnetic properties as a solid phase for separating biological mixtures. The particles are coated with a biological material. They are suitable, for example, for separating off defined cell populations from a mixture of different cell populations.
U.S. Pat. No. 4,795,698 discloses a process for preparing suspendable magnetic particles coated with a biological material. In that process, a coprecipitation is carried out from a solution comprising Fe(III) ions and a polymer, e.g., a protein, by addition in the case [sic] of a strong base, such as NH4OH. The coprecipitate is resuspended, washed and then processed further to give a magnetic polymer material. The process has the disadvantage that iron ions are released.
The object of the present invention is to eliminate the disadvantages of the prior art. In particular, the intention is to provide magnetic particles, which are easy and inexpensive to prepare, for separating biological mixtures.
In accordance with the invention, magnetic particles, for separating biological mixtures, are provided which comprise pearl luster color pigments having magnetic properties and a biological polymer coating. Pearl luster color pigments are inexpensive base starting materials which are produced on the industrial scale in particle form for the coatings industry. They comprise mica leaflets, possibly with a coating of various metal oxides, such as hematite or titanium oxide.
In the case of magnetic pearl luster color pigments, a mica core is enveloped first with titanium oxide and then with magnetite. This so-called black pigment possesses ferromagnetic properties. It is available in particle size distributions of typically 10-60 xcexcm, preferably in particle sizes of 1-30 xcexcm. The black pigment typically has the following composition:
mica 38-48% by weight
titanium dioxide 5-9% by weight
magnetite 47-53% by weight
The black pigment can, surprisingly, be coated directly with biological polymers. In this form it is suitable for separating biological mixtures.
A further surprising property of the magnetic pearl luster color pigments is their resistance to acids, such as glacial acetic acid, alkalis, such as sodium hydroxide, and to organic and inorganic solvents, such as dimethyl sulfoxide/water mixtures, acetone, alcohols, cellulose thinners, methylene chloride and the like. The magnetic behavior of the particles of the invention is unaffected by the aforementioned substances.
The particles of the invention are preferably employed in combinatorial chemistry and in high throughput screening. They can be used in particular as solid phase supports for organic reactions.
In the case of reactions requiring extreme solvents, the biological polymer coating is not resistant. It has surprisingly been found that black pigments can be used as solid phase supports in combinatorial chemistry or in high throughput screening. They can be used, further, as catalysts.